This disclosure relates to a damper assembly and specifically a multi-stage switchable inertia track assembly.
Automotive engineers frequently use hydraulically damped elastomeric powertrain mounts to control shake and vibration responses resulting from various sources such as road inputs. This commonly comes in the form of a rubber isolator containing a hydraulic fluid cavity which acts as a pump when excited by vibration. The pumped fluid oscillates through a tube called an inertia track which creates a fluid resonance system and associated damping to dissipate the vibration energy and reduce the shake response. It is often desired to have a “bypass valve” designed into the fluid system to allow the pumped fluid to bypass the inertia track and flow directly into a low pressure reservoir under certain conditions, typically low amplitude vibrations, such as engine idle speed inputs, where isolation rather than damping is preferred to eliminate vibration. This bypass valve usually takes the form of a simple rubber disc or other flat shape, fitted between two perforated rigid forms, such as pierced metal plates, which is positioned to provide a short, direct route to the low pressure reservoir. Clearance between the thickness of the disc and the spacing of the perforated plates permits unimpeded flow between the pump chamber and low pressure reservoir for small vibration inputs, while effectively sealing the pathway and forcing the fluid to flow through the inertia track during high amplitude vibration. The disc or other shape that redirects fluid flow depending on the amplitude of the vibration input is referred to as the decoupler.
The basic technology for switchable hydraulic engine mounts has been known in the industry for several years, and commonly owned published applications WO2009105768A1 and WO2010/080630 show and describe representative engine mount assemblies. Physical switching of a hydraulic mount from a fluid damped state to a non-damped state by way of opening and closing a port is well understood. However, there are multiple methods by which this can be achieved.
Most vacuum actuated hardware is mounted externally for ease of manufacture. This external mounting tends to reduce the efficiency of the mount response. Most conventional designs use a diaphragm that encloses a volume and forms an air spring under the diaphragm and attached to an external port. Opening and closing this external port is the method used to “switch” the mount state, i.e., the stiffness or damping response. In the switch “open” state, air can be pumped to atmosphere from the volume. For example, the hydraulic engine mount has a low bearing spring stiffness with the open switch (the volume is open to atmosphere) and the engine mount damps or insulates idling vibrations (low amplitude, high frequency). In the switch “closed” state, the air in the volume acts as a stiff spring because the volume is closed or sealed and the damping fluid is transferred back and forth between a first or working fluid chamber and a second or compensating fluid chamber to damp high amplitude, low frequency vibrations. The air spring (closed volume) created by the closed port reduces the pressure of the fluid that would otherwise be pumped through the inertia track, as some of the fluid pressure is used to compress the air spring.
As with most switchable hydraulic engine mounts, this mount is intended to suspend the powertrain, provide damping to powertrain motion, control the powertrain travel, and isolate the powertrain from the vehicle chassis. The switch mechanisms in multi-state mounts allow the mount to switch among four states. Two of the states allow the fluid effect of the mount to be decoupled from compliance vibrations, and the other two states adjust the damping and frequency response of the mount.
A need exists for an improved switchable inertia track assembly, an associated method of packaging same, a design that functions in the same manner as a vacuum actuated multistate mount, but instead of vacuum, uses solenoids to switch the states, and also functions as a decoupled hydromount if there is an electronic failure.